A polymer-dispersed type liquid crystal display device disperses liquid crystals into polymers and uses the scattered light. This liquid crystal display device does not need a polarizing plate so it can provide a clearer picture compared to a TN type liquid crystal display device. Therefore, the polymer-dispersed type liquid crystal display device has been actively developed. FIG. 13 shows an example of a conventional polymer-dispersed type liquid crystal display device. In this drawing, 51 is a polymer-dispersed liquid crystal (PDLC) layer, 52 is a transparent substrate, 53 and 54 are transparent electrodes, 55 is a photo-absorbing plate, and 56 is a color filter.
The liquid crystals dispersed into the polymer base material are arranged disorderly, or they are in a scattered state. When voltage is applied between the pair of transparent electrodes (53, 54) which face each other across the PDLC layer 51, the liquid crystals become orderly, namely transparent. The process can be reversed. The transparent electrodes 53 and 54 are constructed to have picture elements formed on the transparent substrate 52.
The liquid crystal display device displays pictures using external light like natural light or indoor light. The light beam entering through a color filter 56 passes the PDLC layer 51 and is absorbed by the photo-absorbing plate 55 when the picture elements are transparent. So, the observer sees the light as black. The light that enters the scattered picture elements (the shaded portion) is partly scattered, and passes the color filter 56 again to outgo at a wide angle. So the observer sees it as colored light.
FIG. 14 shows another well-known example of a conventional three-dimensional (3-D) picture display device, in which a lenticular lens 57 and a display device 58 are combined. The lenticular lens 57 is constructed by arranging a number of long and narrow cylindrical lenses. The lenticular lens is disposed in front of the display device 58 like a CRT or a liquid crystal display.
The picture image shown in the display device 58 is divided into pairs of frames arranged alternately in a stripe pattern. The plain-colored stripes constitute first frames 59 while the shaded stripes constitute second frames 60.
When the first frames 59 display a parallax picture for a right eye and the second frames 60 display a parallax picture for a left eye, the parallax picture for the left eye is caught only by the left eye of an observer at a predetermined position, while the parallax picture for the right eye is caught only by the right eye of the observer, due to the function of the lenticular lens. For the observer 61, the picture image seems to appear on the display screen like a 3-D picture.
However, such a conventional liquid crystal display device only provides a picture with inferior luminance because of the following reason. As shown in FIG. 15, the light beam enters, passes the PDLC layer, and forms scattered light. This is generally known as front scattering. Back scattering is a scattering to the back side (incident side). In a PDLC layer, back scattering never exceeds front scattering. According to the conventional technique, more than half of the light which enters scattering picture elements is absorbed by the photo-absorbing plate 55. Therefore, the luminance of the picture is always low, and it is difficult to constitute a direct-view display.
In addition, the PDLC layer 51 and the transparent electrodes (53, 54) are sandwiched by the photo-absorbing plate 55 and the color filter 56. Even if the PDLC layer 51 becomes transparent because of voltage application, this property cannot be fully utilized. Further, it is impossible to display 3-D pictures with the conventional structure. The 3-D picture display device in FIG. 14 needs a lenticular lens, so the device cannot provide a transparent display picture.